Vol. 5, No. 7 , July 1966
COORDINATION COMPLEXES OF THE SELENOCYANATE ION 1113
for providing facilities and for helpful discussions. Decoupling and variable-temperature nmr studies done by Varian Associates are gratefully acknowledged.
The author also wishes to acknowledge the support of the Washington University computing facilities through NSF Grant G-22296.
CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY, UNIVERSITY OF DELAWARE, NEWARK, DELAWARE19711
Coordination Complexes of the Selenocyanate Ion1 BY JOHN L. BURMEISTER
AND
LLOYD E. WILLIAMS
Received February 4 , 1966 A series of new selenocyanate complexes of transition metal ions has been prepared. The basic preparative technique involves the reaction of the appropriate metal salt with potassium selenocyanate and [(n-C4Hg)4N] SeCN in absolute ethanol. The complexes were characterized by elemental analyses, conductivity measurements in nitrobenzene solution, and infrared spectra of Nujol mulls and acetone solutions. Examples of both bonding modes of the selenocyanate were found: [M(NCSe)4I2- ( M = Fe(II), Zn(II)), [M(NCSe),ln- ( M = Mn(II), Fe(III), Ni(II), Y(III)), [Rh(SeCN)6I3-, and [M(SeCN)4I2- (M = Pd(II), Pt(I1)). The Cd(I1) complex prepared is unique in its constitution, [(n-C4Hg)4N]2[Cd2(NCSe)6]. Its infrared spectrum supports a structure involving Cd-NCSe-Cd bridges and terminal Cd-XCSe groups. The ranges of integrated absorption intensities of the C-N stretching bands for Se- and N-bonded complexes were found to be, respectively, 0.5-1 X lo4 and 5-10 X lo4 M-' cm-2. The visible spectrum of the Pd('I1) complex indicates that the ligand field strength of -SeCN is less than that of -SCN, the former being slightly below -Br in the spectrochemical series.
Introduction
cipitated was removed by filtration, the desired product was precipitated from solution by the addition of ethyl ether. The coordination chemistry of the selenocyanate ion Selenocyanate Complexes.-The preparative technique emwas, until this decade, an area almost completely devoid ployed was essentially the same for all of thc complexes, with the of research. Recent studies2-6 have emphasized the exception of those of Y(II1) and Rh(II1). To a solution of the hydrated metal nitrate (Fe(III), Ni(II), Zn(II), Cd(II)), sulfate analogous coordination behavior of the selenocyanate (Fe(II)), chloride (Mn(II)), or complex chloride (Pd(II), Pt(I1)) and thiocyanate ions. However, a t the inception of in absolute ethanol was added an ethanolic solution of a stoichiothis study, complexes containing selenocyanates as metric amount (with respect to metathesis) of KSeCN. The rethe only ligands had been prepared for only five difsulting mixture was filtered into an ethanolic solution of the calferent transition metal ions: [ C O ( N C S ~ ) ~ ][Cr~ - , ~ ~culated ~ amount of [(n-C4HB)*N]SeCN,and the solution thus obtained was stored a t -20' until the complex crystallized. The (NCSe) 6]3-,5 [Pt(SeCN)el2--, [Hg(SeCN)4 12-, and crystals were isolated by filtration, washed with absolute ethanol AgSeCN (bridged).2 In an effort to obtain a more and anhydrous ethyl ether, dried in vacuo, and recrystallized from complete picture, we have synthesized a number of absolute ethanol. Water was added initially to dissolve the hitherto unknown selenocyanate complexes. As this Fe(II), Pd(II), and Pt(I1) salts completely. The Ni(I1) compaper was being written, Forster and Goodgame7 plex was first precipitated by the addition of anhydrous ethyl ether. The initial Pt(I1) reaction mixture was warmed gently published the results of a study involving selenocyanate on a steam bath in order to complete the substitution reaction. complexes of several transition metal ions which we The Y(II1) and Rh(II1) complexes were prepared by the direct had included in our work. However, no two of the reaction in ethanol of, respectively, Y(NO~)~.BHzO and K3[Rhcompounds prepared from ions common to both studies Cl6] .H20 with excess [(n-CaH9)4N]SeCN. Water was added to are identical and the results are, on the whole, complecomplete the dissolution of the Rh(II1) salt. The reaction mixtures were warmed on a steam bath to complete the reactions, mentary. then cooled in an ice bath and treated as above. Experimental Section Infrared Spectra.-Infrared spectra, in the 4000-400 cm-I range, of complexes held in Nujol suspension between KBr plates Preparation of Compounds. [(n-C4H9)4N]SeCN.-This salt were measured on a Perkin-Elmer Model 421 recording spectrowas prepared metathetically from the corresponding bromide and photometer. The same instrument was used to record highKSeCN in ethanol. After the potassium bromide which preresolution spectra of Spectro Grade acetone solutions of the complexes in the selenocyanate C-N stretching range (2200-2000 cm-I). Matched 0.1-mm NaCl cells were employed. (1) Presented in part a t the Symposium on Coordination Compounds, sponsored by the University of Padova, Bressanone, Italy, July 26-29, 1965, The integrated absorption intensities, A (M-I cm-z)), of the and at the 151st National Meeting of the American Chemical Society, PittsC-N stretching bands were determined by Ramsay's method of burgh, Pa., March 22-31, 1966. direct integration.s Beer's law plots were made for all of the (2) A. Turco, C. Pecile, and M. Nicolini, PYOC.Chem. Soc., 213 (1961); solutions. J . Chem. Soc., 3008 (1962). (3) S. M. Nelson, Proc. Chem. Soc., 372 (1961). Visible and Ultraviolet Spectra.-Visible and ultraviolet ab(4) F. A. Cotton, D. M . L. Goodgame, M. Goodgame, and T. E. Haas, sorption spectra of ethanolic solutions of complexes were measured ~~
Inorg. Chem., 1, 565 (1962). ( 5 ) K. Michelson, Acta Chem. Scand., 11, 1811 (1963). (6) M. E. Farago and J. M. James, Inorg. Chem., 4, 1706 (1965). (7) D. Forster and D. M . L. Goodgame, ibid., 4, 1712 (1965).
(8) D. A. Ramsay, J. Am. Chem. Soc., 14, 72 (1952).
1114
JOHN
L. BURMEISTER AND LLOYD E. UT IL1,IAMS
Inorganic Chemistry
I
TABLE I FORMULAS, COLORS, YIELDS,MELTINGPOISTS,MOLARCONDUCTANCES, A N D ANALYTICAL DATA Analyses, 70---~-----Yield,
Calor
Compounda
ohm-1 cm-2
Up, ‘
70
~
b
mole-’
-----
----Theory---C
H
-----p C
N
ound-----
x
H
Rd[Mn(SCSe)6] White 22 85 90 50.81 8.77 8.46 50.62 8.50 8.67 45.01 7.55 8.75 45.19 7.62 8.96 R~[Fe(PicSe)~l Light tan 64 80 49 Rs[Fe(KCSe)e] Reddish browii 46 78 66 45.90 7.70 8.92 45.75 7.6t3 8.73 Rr[Xi(^UCSe)e] Dark green 49 121“ 98 50.69 8.i5 8.49 49.98 8.44 8.63 RP[ Zn(NCSe1 4 1 White 44 60 51 44.56 7.48 8.66 44.79 7.57 8.67 R3[Y(NCSe)d White 59 159 68 44.85 7.53 8.72 44.95 7.70 8.90 g 3 [Rh(SeChT)e] Dark red 52 e 70 44.42 7.46 8.63 44.20 7.35 8.48 R2[ Pd(SeCS)r] Reddish brown 92 e 52 42.76 7.18 8.31 42.98 7.21 8.35 RP[Cdn(KCSe)c] White 70 119d 42 34.07 5.42 8.37 34.11 5.45 8.48 R2[ P t (SeCX)J Reddish brown 55 132 52 39.31 6.60 7.64 39.10 6.46 7.64 R = [ ( n - CdHy)jS]+. Uncorrected. Philiips and Tyree [D. J. Phillips and S. Y. Tyree Jr., J . A m . Chem. SOC.,83,1806 $T): 1:1,20-30; 2:1,40-60; 3:l (extrapolated), (196l)l give the following ranges for molar conductauces in nitrobenzene (25”, 60-90; 4:1 (extrapolated), 80-120. Melts with decomposition. 6 Softening, tacky range with transition to melt. f This coinplex has recently been prepared by Schmidtke [H.-H.Schmidtke, private communication]. g Calcd: Se, 35.37. Found: Se, 35.00. ii Calcd: P t , 17.73. Found: P t , 17.69.
‘ Q
TABLE I1 INFRARED DATAFOR THE COMPLEXES COmDoUndn
C-Se str, u l ( S e C N ) , cm-1
S e C S bend, vi(SeCS), c m - 1
_--
Auiin,b
va(SeCN), cm-1
RI[M~(SCS~)O]
640 vn-, 617 w
424 m
R P[Fe(iYCSe),]
673 sh 666 rv
432 ni
Rj [Fe(XCSe)e]
673 S h , 666 \v
431 m
Ra [ Ni (NCSe)b]
623 w
430 In
661 m
429 m
634 m
429 m
515 w
d
519 w
d
589 sh, 582 m
417 w,408 m
516 w
d
--__
C-N stretch
2097 sh, 2082 s,br, 2070 s, br 2064 s, br 2067 s, br, 2055 sh 2064 s, br 2067 s, br, 2055 sh 2061 s, br 2118 sh, 2102 s,br 2100 s, br 2070 m, br 2087 s, br 2087 s, br 2067 s, br, 2030 sh 2068 5 , br 2104 s, sp, 2071 m, sp 2107 S, sp 2107 s, sp, 2060 w 2113 s, sp 2125 sh,2109 s,br 2120 5 , spe 2076 s,brf 2105 s,sp,2060 w 2117 s, sp 2068 s, sp 2067 s,sp
cm-1
elnrxiC
31-1 cm-1
10 -‘A
,c
J - 1 cm-2
8.7
26
920
27
1080
11
27
1050
10
30 20
364 210
4.0 1.5
25
1050
9.5
27
514
5.0
15
176
0.96
10
170
0.82
16 24
557 300
3.2 2.6
13
124
0.59
KSeCN 1.8 16 307 2.1 [ (n-C4H9)4N]SeCN 16 356 a R = [(n-C4H9)&] +. Apparent half-band width. Calculated per mole of coordinated selenocyanate. Concentration of all solutions used was 5 X il/l (with respect to coordinated selenocyanate). d No band found down to the scanning limit (400 cm-l). e Assigned to bridging selenocyanates. f Assigned to terminal selenocyan+tes (see text). Abbreviations: (M), complex held in Nujol suspension; (S), acetone solution; s, strong; ni, medium; w, weak; br, broad; sp, sharp; sh, shoulder. on a Perkin-Elmer Model 202 recording spectrophotometer using matched l.O-cni quartz cells. Conductance Measurements.-Molar conductances, a t 25’, of 10-3 All solutions of the complexes in Fisher Certified Reagent grade nitrobenzene were measured with an Industrial Instruments, Inc., Model RC-16B2 cotiductivity bridge and a cell with platinized electrodes. Analyses.-Carbon, hydrogen, and nitrogen microanalyses were performed by the Alfred Bernhardt Microanalytical Laboratory, Miilheim, Germany. Selenium was determined gravimetrically after precipitation with hydrochloric acid and hydroxylammonium chloride.$ Platinum was determined gravimetrically by igniting a weighed sample of the compound in a porcelain crucible over a Meker burner. (9) A . I. Vogel, “A Textbook of Quantitative Inorganic Analysis,” 3rd ed, Longmans, London, 1061, p 509.
The formulas, colors, yields, melting points, molar coiiductances, and analyses for the complexes are shown in Table I.
Results and Discussion Representative infrared spectra are shown in Figures 1 and 2 ; the infrared data for all of the complexes are given in Table 11. The ultraviolet and visible absorption maxima for the selenocyanato and thiocyanatolO complexes of rhodium(II1) , palladium(I1) and platinum(I1) are given in Table 111. The complexes were formulated with respect to the bonding mode of the selenocyanate ion on the basis of )
(10) C K Jfirgensrn, “Absotption Spectra and Chemical Bonding in Complexes,” Pergamon Press, London, 1962, pp 196, 287, 288, 296.
COORDINATION COMPLEXES OF
Vol. 5, No. 7, July 1966
7 00
600 500 Frequency, cm - 1
.
THE
SELENOCYANATE ION 1115
4
2200
2100
2000
Figure 1.-Infrared spectra (Nujol mulls) of: A, [(n-C4Hg)*N]3Pr equency cm 1 [Y(NCSe)d ; B, [(n-CaH9)4N]SeCN; C, [ ( ~ - C ~ H Q ) ~ N ] Z [ P ~ (SeCN)*]; D, [ ( ~ - C ~ H Q ) ~ N ]NCSe)o]. Z[C~Z( Figure 2.-Infrared spectra (acetone solutions, 0.05 M in coordinated SeCN-) of: A, [(n-C4Hs)rN]SeCN; B, [ ( ~ - C ~ H B ) ~ K I ~ TABLEI11 [Y(NCSe)s]; C, [(n-C4H9)4Nl2[Pd(SeCN)4]; D, [(n-CrH~)aNlzULTRAVIOLET AND VISIBLESPECTRA OF [C&(NCSe)61. SELENOCYANATO AND THIOCYANATO COMPLEXES 7 -
Complex
X
Absorption maxima, kK-------x = Sa
= Se
[Rh(XCK)s]338.2,b32.8b 34.5,c 19.4 sh 31.0,b23.2 sh, 18.9 sh 32.5,'24.5 sh, 20.0 sh [Pd(XCN)r]'[Pt(XCN)d]'39.4,b22.2 sh 37.4,
